Radio receiving system



April 17, 1934. N. E. LINDENBLAD 5 RAD IO RECEIVING SYSTEM Filed March23, 1928 II 16 v 14 L 10 PHI/YR 24 14 I n- I 10 E E RECi/Vtk I i lINVENTOR NlLS E. UNDENBLAD RY ATT NEY Patented Apr. 17, 1934 UNITEDSTATES 1,955,245 RADIO. RECEIVING SYSTEM Nils E. Lindenblad, RockyPoint, N. Y., assignor to Radio Corporation of America, a corporation ofDelaware Application March 2 3, 1928, Serial No. 264,130 2 Claims. (01.ZED-20) '10 damped, and also modulated carrier energy, for

the latter is substantially undamped, relative to the high damping ofstrays. It is an object of my invention to reduce stray disturbances byproviding circuits which will discriminate between undamped and highlydamped energy impulses.

Incidentally, such an arrangement aids in preventing interference bycode signals from spark transmitters, which are especially bothersomeowing to their wide frequency band.

Stray disturbances can never be successfully reduced by using tuned.circuits alone, because no matter what the arrangement is, as soon asthe disturbance has entered a tuned circuit it sets up an oscillation,and will stay there until it is able to pass on to other circuitscoupled to it, or is absorbed by the resistance of the first circuit,for each disturbance represents a certain amount of energy which must bedissipated before it will disappear. It has been suggested to useresistances in the receiving circuit to aid in the dissipation of thedisturbance, but the use of simple resistances alone does not change thesignal to stray ratio, while the use of resistances in tuned circuitshandicaps the reception of the desired signal, and permits disturbancesto reach the tuned circuits, where their effect may be noticed perhapslong after the stray has entirely passed by the receiving station.

The object of my invention is to reduce stray 4o disturbance bydiscriminating between undamped ranged in series with an absorptionresistance of the order of magnitude of the impedance of the tunedcircuit for energy of the resonant frequency. The inert circuit iscoupled in series with an aperiodic antenna, so that the impulsesapplied to it are a true copy of the electrical waves in space, and thereceiver is coupled, to the resonant circuit of the electrically inertcircuit. In this way most of the initially received energy is absorbedin the resistance, but the remainder is efiiciently resonated, so thatundamped synchronous energy is built up. 7

The invention is more fully described in the following specification,which is accompanied by a drawing in which Figure 1 indicates myinvention as applied to a wave antenna, which is most desirable; and

Figure 2 shows its application to an aperiodic loop antenna.

Referring to Figure 1 there is a wave antenna 2 grounded through a surveresistance 4, and coupled to an electrically inert-circuit 6 through anintermediate coupling tube 8. The coupling tube serves to block theinert circuit and receiver circuits from the wave antenna, so that thelatter may be kept practically perfectly aperiodic.

The inert circuit 6 comprises a parallel resonant circuit 10, which istuned to the desired signal, and an absorption resistance 12, which ispreferably of the order of magnitude of the parallel impedance of thecircuit 10 to energy of resonant frequency. 1

The receiver 14 is suitably coupled to the tuned circuit 10. In thepresent case the connection is made through the medium of anothercoupling tube 16, the grid of which is blocked from the p high potentialon the anode of the tube 8' by means of a blocking condenser 18, and thebias of which is established by means of a grid leak resistance 20.

When subjected to a sudden impulse the action of the inert circuit maybe explained] as follows. In transient behavior, in series with the highresistance 12, the condenser of the tuned circuit 10 has zero reactance,and the inductance has infinite reactance, and they cannot be brought toequal values for parallel resonance with its resulting high impedanceexcept by the application of sustained oscillations. It follows that fora sudden impulse the impedance of the inert circuit 6 is practicallyentirely that of the absorption resistance 12, so that the potentialapplied to the inert circuit is spent practically entirely in theresistance 12, and practically no potential is applied to the grid ofthe coupling tube 16, for that is coupled below the resistance. However,when sustained oscillations from a continuous wave signal are applied tothe system the slight impulses which leak through the resistonce 12gradually build up in the circuit 10 and cause it to have a highimpedance of magnitude comparable with that of the resistance, so thatfor undamped oscillations a substantial portion of the inert circuit 6is the impedance of the tuned circuit 10. The potential across thiscircuit is directly applied to the coupling tube 16, and serves toenergize the receiver. In this Way the ratio of response to energy whichis highly damped, and to sustained oscillations, is made enormouslydifferent. If, on the other hand, a voltage produced in the antenna isapplied directly across a tuned circuit without a resistance in seriesthe tuned circuit will respond to even a sudden impulse, because theenergy from a sudden impulse charges the condenser, and causes sustainedoscillation in the tuned circuit, instead of being dissipated in theresistance.

Figure 2 shows how the inert circuit 6 may be used to couple a receiver14 to an aperiodic loop 22. The inert circuit is simply placed in serieswith the untuned loop, and the receiver is coupled to the timed circuitof the inert circuit. In the present case inductive coupling has beenshown, and preferably a' grounded ast'atic shield 24 is provided betweenthe coils of the coupling transformer.

Experiments with this inert circuit show that communication may becarried on even through heavy lightning storms which make receptionimpossible with an ordinary tuned receiver. The reception is best forplain continuous wave signals, and is slightly worse for signals whichare somewhat damped, like the modulated carriers of broadcastingstations. Spark reception is efiectively prevented unless the couplingis made very strong.

Even an aperiodic loop is somewhat reactive and will store some energy,but a wave antenna is ideally combined with my inert circuit, for it isnon-reactive, owing to its surge resistance termination, and thereforepossesses no electrical inertia.

I claim:

1. In receiving apparatus, a wave antenna, a resistance connectedbetween one terminal of said antenna and ground, a thermionic repeaterhaving anode cathode and grid electrodes, means for connecting saidcathode and grid electrodes to the terminals of said resistance, aninductance and variable capacity connected through a resistance to saidanode, a second thermionic tube having its grid electrode connectedthrough a capacity to the connection between said resistance and saidinductance, and indicating means connected with the output electrodes ofsaid last named tube.

2. Receiving apparatus comprising a wave antenna, a surge resistanceconnected between said antenna and ground, a thermionic coupling tubehaving its control grid connected to one terminal of said resistance andits cathode connected to ground, an absorption resistance connected tothe anode of said tube. an efficient parallel resonant circuit havingone terminal connected to said resistance and the other terminalconnected by way of a capacity to the cathode of said tube, a receiver,and'a thermionic repeater having its output electrodes connected withsaid receiver and its control grid electrode connected to the terminalof said parallel resonant circuit, which is connected to said absorptionresistance.

NILS E. LINDENBLAD.

